A quality control method by ultrasonic vibration energy and diagnosis system at trimming process

Abstract

To investigate a relation between vortex clusters and large-scale structures in the outer layer of wall turbulence, direct numerical simulations of turbulent channel flows have been conducted up to Re τ = 1270. The vortex clusters in the outer layer consist coherent fine scale eddies (CFSEs) of which diameter and maximum azimuthal velocity are scaled by the Kolmogorov length and the Kolmogorov velocity. The CFSE clusters are inside the large-scale structure, which contributes to the streamwise velocity deficit. The scale of those clusters tends to be enlarged with the increase of a distance from the wall. The CFSE clusters are composed of the relatively strong CFSEs, which play an important role in the production of the Reynolds shear stress and the dissipation rate of the turbulent kinetic energy. The most expected maximum azimuthal velocity of the CFSEs in these low-momentum regions of the outer layer is 30 ~ 70% faster compared with those of the CFSEs in unconditioned regions (i.e. all regions of the outer layer), while the most expected diameter of the CFSEs is not changed greatly.